The invention relates to a bandgap reference circuit which produces a reference voltage that is temperature compensated. An enable signal input can be employed to render the circuit in either its active or inactive state.
An early threshold detector based upon a reference circuit is disclosed in Stanojevic U.S. Pat. No. 4,701,639. This patent issued Oct. 20, 1987, is assigned to the assignee of the present invention and its teaching is incorporated herein by reference. In this invention an output signal is provided as a function of an applied voltage. The threshold voltage is based upon a temperature compensated bandgap circuit of known construction.
The temperature compensated bandgap circuit is of the configuration disclosed by A. Paul Brokaw in the IEEE Journal of Solid-State Circuits Vol SC-9, No 6, Dec. 6, 1974, (pages 388-393). The paper is titled "A Simple Three-Terminal IC Bandgap Reference". The teaching in this paper is incorporated herein by reference.
In the Brokaw circuit two transistors are operated at ratioed current densities to develop a differential base to emitter voltage (.DELTA.V.sub.BE). The emitters are coupled together and a resistor is incorporated in series with the emitter of the low current density transistor. The high density transistor emitter is returned to the power supply terminal by way of a second resistor. The collectors of the two transistors are returned to the other supply terminal. The transistor bases are coupled together and are operated at a potential that is equal to the silicon bandgap extrapolated to absolute zero. The base voltage is composed of a positive temperature coefficient portion that appears across the second resistor in series with a negative temperature coefficient voltage which is due to the V.sub.BE of the high current density transistor.
When using the Brokaw configuration in the Stanojevic threshold detector circuit a temperature compensated threshold reference is available. However, the reference voltage is not available as an output. One of the attributes of the Stanojevic circuit is that the circuit is powered from, and all of the circuit current flows from the control terminal.